Query interface basics in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the Rails Query Interface?

It allows you to ask the database for specific data using simple Ruby methods instead of writing raw SQL.

beginner

How do you get all records of a model called Book using the Rails Query Interface?

Use Book.all. This returns all the books stored in the database.

beginner

What does Book.where(author: 'Alice') do?

It finds all books where the author is 'Alice'. It returns a collection of matching records.

intermediate

Explain the difference between find and find_by in Rails Query Interface.

find looks up a record by its ID and raises an error if not found. find_by searches by any attribute and returns nil if no record matches.

intermediate

What does chaining queries mean in Rails Query Interface?

It means combining multiple query methods like where, order, and limit to build a precise database request step-by-step.

Which method returns all records of a model in Rails?

A select

B find_by

C all

D where

all returns all records of the model.

What does Book.where(published: true) return?

A An error

B All books

C The first book published

D Books where published is true

It returns books with the attribute published set to true.

Which method raises an error if no record is found by ID?

A find

B find_by

C where

D all

find raises an error if the record with the given ID does not exist.

How can you get the first record matching a condition?

A find_by

B Both B and D

C all.first

D where.first

Both where(...).first and find_by(...) return the first matching record.

What does chaining Book.where(author: 'Bob').order(:title).limit(3) do?

A Finds 3 books by Bob ordered by title

B Finds all books ordered by title

C Finds 3 books ordered by author

D Returns an error

It finds up to 3 books where author is 'Bob', sorted by title.

Describe how you would use the Rails Query Interface to find all records where a condition is true and sort them by a column.

Think about combining methods step-by-step.

Explain the difference between find and find_by in Rails Query Interface and when to use each.

One is strict and the other is more flexible.